1. Field of the Invention
The present invention relates to acetoacetic acid arylide type disazo pigments and to pigment dispersions thereof. More specifically, the present invention relates to an acetoacetic acid arylide disazo type pigment and to a pigment dispersion, which is useful in various applications, including coloring materials such as ink, paint, plastic, color toner, and color filter.
2. Description of Related Art
C.I. Pigment Yellow 180 including 2,2xe2x80x2-[1,2-ethanediyl-bis(oxy 2,1-phenyleneazo)] bis [N-(2,3-dihydro-2-oxo-1H-benzimidazole-5-yl)-3-oxo-butaneamide (hereinafter referred to as a basic substance) is known as a useful yellow colorant, and has been used for various purposes. The basic substance can be obtained by a diazocoupling reaction, and since it has the structure derived from one of the raw materials, i.e., a benzimidazolone compound, the pigment has significantly high light fastness, improved overcoating fastness when applied to paint, and improved migration fastness and high thermostability as applied to a synthetic resin. The term xe2x80x9cpigmentxe2x80x9d, in contrast with the definition of a dye, means, in its broader application, fine powder which does not dissolve or is insoluble in water or organic solvent. This also applies to the above basic substance. In the present invention, in accordance with the above definition, a crude pigment, which will be described later, is also included in pigments.
Also, since 1,2-bis(2-aminophenoxy)-ethane, not dichlorobenzidines which are mutagenic, is used as the raw material for a bisdiazonium salt, which is the other substance used for the diazocoupling reaction, in the production of the basic substance, C.I. Pigment Yellow 180 is one of the few yellow colorant among acetoacetic acid arylid disazo type agents that can be used for, for instance, a preparation for electrostatic image developing toner, to which xe2x80x9cBlauer Engelxe2x80x9d (long title: xe2x80x9cDas Umweltzeichenxe2x80x9d meaning xe2x80x9cenvironmental protection labelxe2x80x9d, a German ecological mark) certified by the German Confederation Environment Agency and operated by German Quality Assurance Label Association, is issued.
Japanese Unexamined Patent Application, First Publication No. Sho 56-38354, Japanese Unexamined Patent Application, First Publication No. Hei 8-209017, and Japanese Unexamined Patent Application, First Publication No. Hei 8-295815 disclose C.I. Pigment Yellow 180 containing the above basic substance.
Despite the above-mentioned broad definition of pigment, all of the conventional manufacturing methods for C.I. Pigment Yellow 180 described in these publications include a first process in which a bisdiazonium salt of 1,2-bis(2-aminophenoxy) ethane is coupled with 5-acetoacetylamino-benzimidazolone to obtain crude pigment, and a subsequent second process in which the crude pigment obtained in the first process is filtered and added to a liquid medium containing organic solvent as an essential component. Then, the liquid medium is subjected to a heat process and a colorant is produced.
Note that in this field of industry, the above-mentioned xe2x80x9ccrude pigmentxe2x80x9d has the same meaning as xe2x80x9cprepigmentxe2x80x9d and xe2x80x9ccrudexe2x80x9d. Likewise, the above-mentioned second process is also referred to as an aftertreating process, a finishing process, a conditioning process, or a pigmentization process. All of these terms have the same meaning.
On the other hand, the BET specific surface area based on the nitrogen absorption method, and the strength of each diffraction peak of a crystal based on Bragg angles measured by using CuKxcex1 characteristic X-ray are examples showing important physical characteristics of pigment. These characteristics, together with the particle size of the pigment, are often used as indices for estimating characteristics of the pigment, such as the readiness of being dispersed in a dispersion medium, for example, vehicle, and the flow properties of a colored dispersion medium obtained.
In C.I. pigment Yellow 180 including the above mentioned basic substance, the particle size of the pigment affects various properties of a dispersion medium colored by using the colorant, such as brightness, transparency, color strength, hue, and flow properties, in the application of printing ink, for example. As for the pigment which has been subjected to the above second process, the smaller the particle size of primary particle thereof, the more its brightness, transparency, and color strength tend to increase. The reason for this is because, in the pigment whose degree of aggregation among particles is smaller (or weaker) than that of a crude pigment, which will be described later, the dispersibility of the primary particle thereof in a dispersion medium to be colored is better. In such a pigment, aggregation of the particles hardly occurs and they can be dispersed in a dispersion medium to be colored in a primary particle level. The measured specific surface area of such pigment having excellent brightness is larger than that of a crude pigment. That is, as for pigment which is subjected to the above second process, there is a tendency that the smaller the particle size of the primary particle of pigment, the larger the specific surface area thereof.
On the other hand, conventional crude pigments including the above basic substance corresponding to C.I. pigment Yellow 180 have lower crystallinity in the primary particle level and smaller particle size than the pigment which is subjected to the second process. Since the primary particles thereof are smaller as compared with the pigment subjected to the second process, the surface energy of the crude pigment is significantly higher, and as a result, the aggregation among the primary particles tends to increase in the crude pigment. Such a strong aggregation of the crude pigment cannot be decreased by using mechanical shearing strength. The specific surface area of such a crude pigment measured in the same manner as the pigment subjected to the second process, is smaller than that of a corresponding pigment. Moreover, if the crude pigment is directly used as a colorant, since the dispersibility thereof in a dispersion medium is insufficient, it is not useful in practice due to such factors as dullness. These are the conventional prevailing views as to the relationships between the physical characteristics of the crude pigment including the above basic substance and its practical applications.
Note that although it is possible to classify the above basic substance into crude pigment, which is not subjected to the second process, and pigment, which is subjected to both the first and the second processes, in the classification based on the manufacturing process as mentioned above, the basic substance is a pigment although it is subjected only to the first process, in the classification based on whether to satisfy various characteristics required for a colorant, regardless of the classification based on the manufacturing process, if it satisfies such characteristics required for a colorant. However, such a basic substance has not been obtained before the present invention.
As in the above conventional prevailing view, the basic substance obtained by the conventional methods described in the above publications is in a strong aggregated state, and the specific surface area thereof is 10 m2/g or less.
A powder X-ray diffraction diagram is a graph in which the strength of X-ray diffraction of a sample at each Bragg angle, when the Bragg angle is continuously changed, is consecutively plotted based on zero of the diffraction strength. The absolute strength of the X-ray diffraction at each Bragg angle can be determined based on zero of the diffraction strength in the powder X-ray diffraction diagram.
The inventors of the present invention paid attention to this point, and newly adopted, as a standard for clearly distinguishing a crude pigment, which is not subjected to the above second process in the classification based on the manufacturing process, from pigment, which is subjected to the above second process, the ratio of the absolute strength of the X-ray diffraction at a Bragg angle 2xcex8=17.5xc2x0xc2x10.2xc2x0 with respect to that at 2xcex8=18.2xc2x0xc2x10.2xc2x0. The inventors of the present invention now found that if a colored dispersion medium is prepared from a crude pigment, which is based on the classification of a manufacturing process, including the above conventional basic substance having the ratio of the absolute strength of  less than 1.8/1.0, its color strength and brightness are not satisfactory and is not suitable for use as a colorant.
For the reasons mentioned above, the crude pigment, which is classified based on the manufacturing process, including the basic substance is not conventionally used directly as a colorant, and is further subjected to the second process mentioned above in order to grow crystals of the primary particles to increase the particle size. In this manner, the aggregation of particles may be loosened and pigment having required brightness and color strength is obtained. Also, the flow properties of a colored dispersion medium are improved. These are all described in the above-mentioned publications.
In the conventional technique relating to the above basic substance, since certain properties required for a colorant can be obtained via the second process as mentioned above, there is no positive motivation in this field to develop a crude pigment, in the classification based on the manufacturing process, which is suitable for application as a colorant. Since the development as a colorant has relied upon the factors in the second process mentioned above, studies have not been made of the use of a crude pigment, in the classification based on the manufacturing process, directly as a colorant.
In addition, in the above-mentioned second process, the aggregation of particles is weakened by growing each particle to increase the particle size of the primary particle. However, when high levels of transparency or color strength is required for an objective application, the inherent small particle size of a crude pigment, in the classification based on the manufacturing process, has an advantage in terms of its transparency. Nevertheless, the particle size of the primary particle is increased in exchanged for weakening the cohesive strength in the second process, and this makes it difficult to obtain expected properties as a colorant.
The inventors of the present invention thought that if the above basic substance is obtained in a weak aggregated state, its specific surface area increases. As a result, the aggregation may be readily loosened by using weaker force to improve its dispersibility, and hence, brightness, etc. If this could be performed, the basic substance, although a crude pigment in the classification based on the manufacturing process, would have characteristics as a colorant.
Accordingly, an object of the present invention is to provide a yellow pigment which can be dispersed using a weak force and can be directly used for applications in which properties, such as brightness and color strength, are important. Another object of the present invention is to provide a yellow pigment which maintains weak aggregated state immediately after a coupling process and includes loosened or easily loosened particle groups.
Also, yet another object of the present invention is to provide a method for manufacturing a yellow pigment having excellent characteristics mentioned above without even carrying out the second process, which is conventionally used for imparting suitable properties as a colorant to the pigment, so that the productivity per unit time of the colorant is improved.
The inventors of the present invention, by fundamental studies on obtaining the above basic substance, which has a weak aggregation state, found that if the basic substance having the specific surface area of 20 m2/g or more is obtained in the above first process, the aggregation state thereof becomes weak, and hence, the color strength and the transparency of a dispersion medium colored by the basic substance having the weak aggregation state are improved even though it should be called a crude pigment in classification based on the manufacturing process.
Also, the inventors of the present invention found that the above basic substance satisfying the condition that the specific surface area and the absolute strength ratio of the X-ray diffraction between two specific Bragg angles are within a specific range, regardless of whether it is classified as pigment or crude pigment in terms of its manufacturing process (i.e., if the above basic substance is prepared via only the first process or both the first process and the second process), and regardless of the classification based on whether it satisfies characteristics required as a colorant (i.e., one which satisfies the characteristics required for a colorant is called a pigment, and one which does not is not called a pigment), has an excellent color strength and transparency and can be called a pigment. The color strength and transparency of a dispersion medium largely changes by the difference in the absolute strength ratio of the basic substance dispersed therein even if the specific surface area thereof is the same.
Moreover, the inventors of the present invention found that the number of steps in the manufacturing process of the above basic substance having the excellent properties may be reduced and the productivity thereof per unit time may be improved since the basic substance, which can be directly applied as a colorant, may be produced via only the above first process without the second process.
In addition, the inventors of the present invention found that the pigment actually obtained via only the first process having the specific surface area of 20 m2/g or greater and a certain range of the absolute strength ratio of the X-ray diffraction between two specific Bragg angles has an excellent color strength and transparency, though smaller in the specific surface area, in comparison with pigment, which is obtained via both the first and the second processes as disclosed in the above-mentioned publications and has the specific surface area of 45 m2/g or greater, under the condition of using the same dispersion medium with the same percentage content. Based on these findings, the inventors of the present invention completed the present invention.
That is, an object of the present invention is to provide a pigment including a chemical compound expressed by the following formula (1), wherein the pigment has the BET specific surface area based on the nitrogen absorption process of 20-100 m2/g, and the ratio of the absolute strength of X-ray diffraction at Bragg angle 2xcex8=17.5xc2x0xc2x10.2xc2x0 to the absolute strength of X-ray diffraction at Bragg angle 2xc2x0=18.2xc2x0xc2x10.2xc2x0 of the pigment in a powder X-ray diffraction diagram using a CuKxcex1 characteristic X-ray is smaller than 1.8/1.0. 
In accordance with another aspect of the present invention, the above pigment further includes a surface treatment agent, the amount of the surface treatment agent corresponding to 0.1 to 50% by weight of the pigment.
In yet another aspect of the present invention, the pigment is used for coloring printing ink, paint, or plastic.
In yet another aspect of the present invention, the pigment is used for coloring toners, or color filters.
According to the pigment described above, since it comprises the above basic substance having the BET specific surface area based on the nitrogen absorption method of 20-100 m2/g and the ratio of the absolute strength of the X-ray diffraction between Bragg angles 2xcex8=17.5xc2x0xc2x10.2xc2x0 and 2xcex8=18.2xc2x0xc2x10.2xc2x0 smaller than 1.8/1.0, it has a remarkable effect in that it can be used as a colorant having excellent transparency and color strength in comparison with conventional pigments having the absolute strength ratio outside the above range. Also, since no aftertreating process for pigmentization is required for the pigment according to the present invention, the number of steps necessary in the manufacturing process can be reduced and the productivity thereof as pigment can be improved. Moreover, the pigment according to the present invention has a superior effect in that it can be used, although crude pigment in the classification based on the manufacturing process, as pigment having better transparency and color strength as compared with pigment subjected to the aftertreating process. In addition, since the pigment dispersion according to the present invention includes the pigment of the present invention having a weaker aggregated state as compared with that of conventional pigments, it has a remarkable effect of providing excellent transparency and color strength.
The present invention also provides a method for manufacturing the above pigment including the step of simultaneously dropping a bisdiazonium salt of 1,2-bis(2-aminophenoxy) ethane and 5-acetoacetylamino-benzimidazolone into an aqueous solution of pH 4-8 to carry out a coupling reaction.
The present invention also provides a method for manufacturing the above pigment including the steps of simultaneously dropping a bisdiazonium salt of 1,2-bis(2-aminophenoxy) ethane and 5-acetoacetylamino-benzimidazolone into an aqueous solution of pH 4-8 to carry out a coupling reaction, increasing the pH of the solution to be higher than the pH of the solution at the completion of the coupling reaction, and heating the solution to a temperature of 60-95xc2x0 C.
The present invention also provides a pigment dispersion including the above pigment, and a thermoplastic resin, wherein 0.5-100 parts by weight of the pigment is dispersed in 100 parts by weight of the thermoplastic resin.
In yet another aspect of the present invention, the above pigment dispersion is obtained by a method including a step of flushing the above pigment including water with the thermoplastic resin.
The present invention also provides an electrostatic image developing powder toner comprising the above pigment dispersion